1. Field of Invention
This invention generally relates to relative movement using small stages, such as stages for micro-electromechanical system (MEMS) devices.
2. Related Art
Improvements in fabrication processes for small devices (such as MEMS devices) are continuing to reduce minimum device sizes. However, small mechanical and electro-mechanical devices pose a number of challenges. For example, it may be difficult to rapidly and accurately move parts of the devices relative to one another.
One important example of a MEMS device is a miniature camera. Miniature cameras are currently available with many electronic devices, such as cellular telephones, laptop computers, personal digital assistants (PDAs), and the like. Miniature cameras are also available as stand-alone devices for applications such as security and surveillance
The market for miniature cameras is rapidly expanding. For example, camera-equipped cell phones were unheard of just a few years ago; now, they are a significant portion of the cell phone market. However, available miniature cameras may not be optimal for some applications.
For example, available miniature cameras may not be optimal because they are fixed focus cameras (i.e., the focus of the cameras is pre-set). By using a relatively small aperture, the depth of field is sufficient to provide acceptable focus over a wide range of distances. However, the provided focus may be unacceptable for some applications. Additionally, the relatively small aperture limits the light used to form the image. This limitation may severely limit the camera's use in low light conditions.
Some miniature cameras use a flash to enhance camera performance in low light conditions. However, the use of a flash consumes more power from the batteries, thus requiring more frequent battery charging.